Synchronizing indicator



y 1943- H. T. SEELEY 2,320,198

smcnnomzme INDICATOR Filed May 2, 1942 Inventorf Harold T Se lea,

His Attorney.

Patented May 25, 1943 ATENT QFFICE 'SYNCHRONIZING INDICATOR Harold TlSeeley, Lansdowne, 'Pa., assignor to 'GeneralElectric Company, acorporation of'Ne'w York Application May 2,

3 Claims.

My invention relates to means for indicating the difference in phaseangle and the magnitude and direction of frequency difference betweentwo three-phase power systems for the purpose of advising an operatorwhen he may safely close a synchronizing switch between such systems. Myinvention also relates to such indicating apparatus of a character bymeans of which the indication may be had at a remote point with theemployment of only two pilot wires or connections. The invention isparticularly useful for indicating at a remote point when a synchonizingswitch in an unattended power station may be safely closed andindicating the direction and extent of change in the frequency or phaseangle to arrive at such condition.

The features of my invention which are believed to benovel andpatentable will be pointed out in' the claims appended hereto. Forabetter understanding of my invention, reference is made in the followingdescription to the accompanying drawing in which Fig, 1 shows thepreferred circuit connections; Fig. 2 representsvector relations andcombinations of the voltages for energizing the instrument; and Fig. 3vector relations for the voltages for energizing a relay employed todeenergize the instrument under certain conditions.

Referring to Fig. l, A and B represent two three-phase power systemswhich are to be connected together by a switch indicated at 10, whichswitch may be remotely controlled. The invention relates to means bywhich an indication is obtained on a single instrument H which may be inthe same station or at a remote station, or there may be similarinstruments at both stations for advising an operator of the phase anglerelation between the two systems and the difference and direction ofsmall differences in frequency, if any, between such systems. Twoinstruments II are shown connected in series, the one to the right beingassumed to be located at a remote point and energized over a pair 'ofpilot wires [2 in order that an operator at such remote point maysynchronize the two systems and close the switch Hi by remote control.The instruments H are preferably of the direct current zero center typeand are energized through rectifiers and potential tranw formers fromthe two systems A and B in a manner now to be described.

For convenience the difierent phases of the power systems are designatedI, 2 and 3. A potential transformer I3 is connected across phases l-3 ofpower system A. This trans- 1942, Serial No. 441,420

former has two similar secondary windings 4 and '5 and produces equalvoltages which I will designate M3 to correspondto phases l and 3 ofpower system A. A potential transformer i4 is connected across phases[-2 of system B and has similar secondary windings 6 and I, the voltageof which will be designated bl'Z. A potential transformer I5 is alsoconnected across phases 2-3 of system B and has similar sec ondarywindings '8 ,andj9, the voltage of which I will designate bl3. When theA and B system voltages are equal, it will be assumed that the voltagesai3, b|2 and 1223 will be equal.

Connections are provided bymeans of which the al3 voltage of secondarywinding 4 and the hi2 voltage of secondary winding 6 are combined tofeed 'the full wave rectifier IS. A portion of the current due to suchrectification may flow out from the top or positive terminal of therectifier and through the instrument circuit as indicated by thesingle-headed arrow and return to the bottom or negative terminal ofrectifier It through resistances l8 and I9 and adjustable potentiometerconnection 21. It will be assumed that when such current flows out fromrectifier 5 it produces a positive indication of the instruments H. TheM3 voltage'of secondary winding 5 is combined with the 1123 voltage ofsecondary winding 9 to feed full wave rectifier bridge i1 and, in caserectifier I! happens to predominate over rectifier I6, a portion of thecurrent from rectifier l 'l flows through the instrument circuit asrepresented by the doubleheaded arrows and causes a negative deflectionof the instruments, the current returning to the bottom terminal ofrectifier ll through resistances 2B and I9 and connection 2!. It isevident that some of the current from a rectifier will not pass throughthe instrument circuit since the instrument. is connected acrossresistance connections l'8l 9 -20 between the positive rectifierterminals. The negative rectifier terminals are also connected together.For example, a portion of the current from rectifier ll will pass fromtop to bottom terminals through resistances l8, l9 and connection 2!.However, bypass resistances l8 and 20 are necessary in order to providea return path for the instrument current. g

I 'he particular rectifier which will predominate to energize theinstrument circuit and determine the direction of the instrumentindication from zero will depend upon theparticular phase angularrelation of the transformer voltages feeding the rectifiers. curves ofFig. 2.

In Fig. 2 the abscissa represents angular phase difference between the Aand B power systems or, more specifically, the degrees lead of system Awith respect to system B starting with zero phase difference at the leftand continuing to the right through a 360-degree range or cycle of suchphase difference. The A and B triangles shown in vertical line with thezero phase difference point represent the in-phase relation of the threephase A and B voltage vectors. Since the B voltage is taken as areference, its triangular representation is assumed to be fixed and isnot repeated. However, the upper line of triangles from left to rightrepresent the A voltage as being rotated counter-clockwise throughsuccessive Gil-degree angles, the positions and orientations of thesuccessive triangles corresponding to the phase difference as indicatedon the abscissa scale. The next lower row of vectors shows thecombination of the al3 voltages with M2 voltages of secondary windings 4and 6 which feed the positive indicating rectifier I6. Thus at phasedifference of the A and B voltages the vectors al 3 and bi 2 are in thesame directions as the vector sides |-2 and |-3 of the A and Btriangles. The dotted line drawn between the terminals of the vectorsrepresents the resultant voltage applied to rectifier l6 for thisparticular phase relation. I call this the positive resultant. At 60degrees displacement vector al3 has rotated in line with vector 1) I 2,and the resultant is correspondingly greater. At 240 degrees the vectorscancel. The third row of vectors shows the manner in which the al 3 andZ223 secondary voltages of windings and 9 combine to feed the negativeindicating rectifier I! for the different angles of lead. At 120 degreesthe resultant is zero, and at 300 degrees the resultant is a maximum, Icall this resultant the negative resultant. If now we should plot thevarious positive resultants, we would obtain a curve such as dotted linecurve P which corresponds to the voltage applied across rectifier It forvarious phase angles between the A and B voltages. Thus at 60 degrees Pis a maximum, and at 240 degrees it is zero. Likewise, if we plotted thedifferent negative resultant voltages or the vector sum of the (113 and1223 voltages as applied to rectifier I1, we would obtain the dottedline curve N. The negative resultants are plotted below and the positiveresultants above the zero voltage line because they are opposed to eachother in the instrument circuit. Thus at 120 degrees N is zero and at300 degrees its negative value is a maximum. The ordinates for thesecurves represent voltage and are so marked in percent. The full linecurve R represents the algebraic sum of curves P and N and correspondsto the resultant voltage applied to the instrument circuit from bothrectifiers. It is seen that at zero and 180 degrees phase difference theinstruments II will read zero. For an angle of lead of phase A withrespect to phase B between zeroand 180 degrees the instrument will Thisis explained by the read positive and for lead angles between 180 and360 degrees the instrument will read negative.

While such instrument information is helpful, it is insufiicient. Forexample, a zero reading does not tell whether the systems are in phaseor 180 degrees out of phase. Also, if the reading be 2'5 per centpositive, the operator does not know if phase A is 30 or 162 degreesahead of B. In the intended use as a synchronizing device the differencein frequency between systems A and B will be small and, as the phaserelations change, the instrument will deflect first positive and thennegative. The rate at which the pointer swings back and forth will be anindication of the difference in frequency between the systems. It willnot, however, indicate which frequency is the higher. As zero frequencydifference is approached and the pointer moves more slowly and finallystops at a given indication, which may be zero, positive or negativewhen the frequency difference becomes zero, the operator cannot be surewhat the phase relation is from such indication and an important aspectof my invention is to modify the character of the indication given bysuch an instrument in order that the direction of frequency differenceand phase relation will be known.

To this end I provide a relay which serves to deenergize the instrumentfor phase angular relations between about degrees and 240 degrees on thescale of Fig. 2. Thus considering the curve R represents plus and minusinstrument reading as well as plus and minus voltage, I modify suchcurve between 120 and 240 degrees as indicated by the dotted line M. Nowwhen synchronism is approached, the instrument pointer will behave verymuch differently between 120 and 240 degrees, as compared to itsbehavior over the remaining part of the cycle of change and the operatorcan readily distinguish between a slow, steady movement of the-pointerthrough zero when passing through synchronism and a sudden drop to zero,a definite pause on' zero and then a sudden deflection while passingthrough the 120 to 240 degree out-of-phase portion of the cycle. Alsonow, if the pointer stops on, say, the 25% plus voltage indication, theoperator knows definitely that system A is leading by 30 degrees and not162 degrees. He knows which way and by how much the phase relation needsto be changed to bring about a paralleling condition and when suchcondition is reached, it is distinguished from the degree out-ofphasecondition by the definitely different manner of approach of the pointerof the instrument to a zero center position. The damping of theinstrument is such as to make this difference stand out. Also now thedirection of the slow motion of the pointer through zero indicates whichsystem frequency is the higher.

One relay arrangement which can be used for deenergizlng the instrumentcircuit over the 120 to 240 out-of-phase portion of the phase relationcycle is shown in Fig. 1. 22 represents a relay controlling a switch inthe instrument circuit. In the example given, the coil of the relay isenergized in accordance with the vector sum of the hi2 voltage oftransformer winding 1, the 2223 voltage of transformer winding 8 and theM3 voltage of transformer winding 4. When the A and B systems are inphase relay 22 receives maximum current and when 180 degrees out ofphase, it receives zero energizing current. The

vector relation for different out-of-phase conditions of these voltagesmay be seen from Fig. 3. The vectors Z742, 1223 and al3 are shown forthe in-phase condition of systems A and B. In this condition, thevoltage across the relay is a maximum and is equal to the diameter ofthe inner circle which is the vector sum of the three voltage vectorsunder this condition. As the phase relation changes through aphase-changing cycle of 360 degrees, vector al3 rotates about-point X.At 120 degrees it is in line with and cancels voltage 1223 so that thevoltage across the relay is reduced to the voltage bIZ.

At 180 degrees it closes the vector triangle and the relay voltagebecomes zero. A From 180 degrees through 240 degrees back to degree therelay voltage increases and at any point is equal to the distance fromthe inner circle at such point to the point marked 180 degrees. Dottedlines indicate the value of the relay voltages at 240, 270 and 300degrees. It is now seen that as thus connected the relay can be readilydesigned to pull up its armature and close the relay circuit over aboutthe 240--0--l20 degree range and to drop out and open this circuitthrough the 120180-240 degree range. Such two ranges are indicated andmarked energized and deenergized on Fig. 3. The exact point on suchcircle where the relay will pull in and drop out is not criticalalthough it should be as near to the points indicated as is feasible forbest results.

It is not important that the relay be designed to function as describedwhen there is a considerable difference in frequency of the powersystems because the operator can tell by the nature of the fluctuationof the instrument pointer and by a knowledge of other conditions if suchconsiderable difierence in frequency exists and does not attempt tosynchronize under such conditions. The relay contacts may be placedanywhere in the circuit or circuits which energize the instrument as,for example, in the connection 2| or the a-c leads to the rectifiers. Itwill be noted that the lead 2| is adjustable along the resistance I9.This calibration adjustment is desirable as a means of setting theinstrument pointer on zero for zero angle where, for example, theinternal resistances of the rectifiers or rectifier circuits do notexactly balance.

It will be evident that this single instrument, when used as intended,gives the operator reliable information as to the direction andmagnitude of phase difference. It distinguishes between the approach tozero and 180 degree phase differences. It also gives an indication offrequency difference and as to which system has the lower frequency. Forinstance, the pointer moves gradually through zero from left to rightbut by jerks in the opposite direction when one system has the higherfrequency and this behavior is reversed if the other system has thehigher frequency. The operator therefore has accurate knowledge as towhen to close the switch "I, and also which system frequency should beraised or lowered in order to arrive at the synchronizing condition. I

In accordance with the provisions of the patent statutes, I havedescribed the principle of operation of my invention together with theapparatus which I now consider to represent the best embodiment thereof,but I desire to have it understood that the apparatus shown is onlyillustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Apparatus for indicating the phase relationship between twothree-phase alternating current systems comprising means for rectifyingthe vector sum of the voltages from one pair of different phases of thetwo systems, other means for rectifying the vector sum of the voltagesfrom another pair of diiTerent phases of the two systems, a zero centerdirect current measuring instrument difierentially connected to the tworectifier means for indicating the direction and magnitude-of thedifference, if any, in said rectified voltages and a phase responsiverelay energized jointly from both systems for deenergizing saidinstrument when the phase relation between said systems is between aboutand 240 degrees out of phase.

2. Apparatus for indicating the phase relationship between twothree-phase alternating current systems comprising transformer means forderiving a first voltage from one phase of one system, transformer meansfor deriving second and third voltages from the other two phases of theother system, connections and rectifier means for rectifying the vectorsum of the first and second derived voltages, connections and rectifiermeans for rectifying the vector sum of the first and third derivedvoltages, a zero center direct current instrument connected to saidrectifier means for producing an indication indicative of the directionand magnitude of the difference, if any, between the rectified currents,and relay means connected to be energized from said transformer means inaccordance with the vector sum of all of the derived voltages fordeenergization of said instrument when the two systems diifer from anin-phase relation by more than about 120 degrees.

3. Apparatus responsive to the phase relation between two three-phasesystems comprising means for deriving a first voltage from one phase ofone system, means for deriving proportional second and third voltagesfrom the other two phases of the other system, a rectified energized bythe vector sum of the first and second voltages, a rectifier energizedby the vector sum of the first and third voltages, a connection betweenthe positive output terminals of said rectifiers, a connection betweenthe negative output terminals of said rectifiers one of said connectionsincluding resistance, a potentiometer connection between said twoconnections and a zero center direct current instrument connected acrosssaid resistance.

HAROLD T. SEELEY.

